tube isolation rings which act as
physical separators preventing the
cells from touching even under
rough flexing conditions. Note: The
temperature ratings of shrink tube
vary, so be sure to investigate
before you purchase. You can cut
individual rings and shrink them
with a heat gun or install a single
piece the length of the cell and use
a razor to remove the center leaving
the two rings (see Figures 2 and 3).

their density, volume, and capacity
when compared to NiMH and NiCds.
However, neither are readily available
in “cell form” making building your
own packs a greater challenge and
one this article will not touch on.

milliamps or 3. 6 amps for one
hour before dropping below
1.0 VDC per cell. They will
produce much higher current
for shorter periods based on
their discharge curve specs.
Cells vary greatly so discharge
curves, as well as other specifications, should be consulted in
the manufacturer’s datasheet.
Note: The desired pack voltage
divided by 1.2 will determine
the number of cells needed in
your pack. For example, a 12

VDC pack would require 10 cells.

Pack Construction —
Let’s Begin!

Selecting Your Cells

Once you have selected your
chemistry (NiMH or NiCd), you will
need to choose a specific cell size
(AA, Sub-C, C, etc.) based on your
application. As a rule of thumb, you
will want to get the highest (mAh)
capacity cells you can afford.

The terms mAh and Ah stand for
“milliamp hour” and “amp hour,”
respectively. A higher mAh rating
means more capacity and longer
runtime. The number preceding
mAh indicates how much DC
current a charged cell will source
for one hour.

For example, the cells depicted
in this article are Sanyo 3600 mAh
NiCd C cells. This means that when
fully charged, they will source 3,600

Roughing Up the Cell Terminals
The first step is a light

“roughing up” of the cell terminals
which allows for a better solder
connection when the bus bars are
installed. While this step is optional,
it is recommended if your pack(s)
will be subject to rough conditions.
A Dremel tool with a small carbide
bit (see Figure 1) makes quick work
of this task. A second option for
those without a Dremel is to score
a series of crisscrosses into the
terminals with the tip of a razor.

Cell Layout

The cells need to be arranged
in a manner that allows one cell’s
(+) terminal to be connected to
the next cell’s (-) terminal. These
connections are made with bus bars
and create a continuous series path
from one cell to the next. Each cell
in the series string will add 1.2V.
The most common shape for packs
is two rows with an equal number
of cells in each row. Take your time
figuring this out before continuing.
Highly customized cell layouts can
be another advantage of building
packs yourself!

Installing Cell Isolation Rings

Next, remove the factory cell
covers with a razor blade. Factory
covers cannot withstand high
temperatures and will shrink and
split exposing the cells in a pack
to possible short circuit. To prevent
short circuiting, we will install shrink

FIGURE 3

FIGURE 2

Bonding the Cells Together
Once the cell layout is
determined, we are ready to bond
the cells together. Bonding adds
needed mechanical stability to the
pack. A flexible adhesive that is able
to withstand high temperatures is
needed here. After experimenting
with various types, we felt Shoe
Goo had the best properties
followed by silicone caulk. Shoe-Goo
has simply incredible adhesion
properties. You will
need a fixture to hold
the cells. We use a
simple jig that clamps
the cells between
wooden 1x1s screwed
to a workbench (see
Figure 3). Apply
adhesive between the
cells and allow to dry,
flip the cells and
repeat. Now apply
adhesive to the two
halves to form the